1. Field of the Invention
This invention relates to a novel liquid crystal compound and a chiral smectic C liquid crystal composition containing the liquid crystal compound as a constituent thereof and being useful for liquid crystal display elements.
1. Description of the Related Art
At present, as to liquid crystal display elements, TN (Twisted Nematic) type display mode has been most broadly employed, but as far as the response speed is concerned, such TN type display elements are inferior to emissive type display elements (such as those of electroluminescence, plasma display, etc.). Although various improvements in this respect have been attempted, it appears that improvement to a large extent has not yet been realized. Thus, various liquid crystal display devices based on a different principle from that of TN type display elements have been attempted. As one of such devices, there is a display mode utilizing a ferroelectric liquid crystal (N. A. Clark et al: Applied Phys. lett., 36, 899 (1980)). This mode utilizes the chiral smectic C phase (hereinafter abbreviated to SC* phase) or the chiral smectic H phase (hereinafter abbreviated to SH* phase) of the ferroelectric) liquid crystal, and those having these phases in the vicinity of room temperature are preferred.
These chiral smectic liquid crystal materials may be obtained by blending a plurality of single compounds each exhibiting a chiral smectic phase by itself, but it is known that the materials may be also obtained by adding an optically active liquid crystal compound, preferably a chiral smectic liquid crystal compound to an achiral smectic liquid crystal exhibiting smectic C phase (SC phase), smectic H phase (SH phase), etc.
Various kinds of compounds exhibiting SC phase have already been known, but as to whether or not chiral smectic liquid crystal materials obtained by adding thereto an optically active liquid crystal exhibit superior performances in liquid crystal display utilizing ferroelectricity, no ultimate evaluation thereof has been yet obtained. This is due to the fact that liquid crystal display utilizing ferroelectricity has not yet been technically completed. Thus, in the present situation, it is necessary to test various novel SC materials.